FIFTH GEAR STALLS AND MAKES A LOT OF NOISE WHEN I ENTER IT BUT THE 6TH WORKS JUST FINE.

1999 Mercedes Benz E200 • 62,000 miles

I drive a Mercedes-Benz E200 Classic (W210), (it is manual transmission, 6 speed) the problem is when im driving and I go into the fifth gear the engine makes a loud noise like im in the wrong gear and sort of stalls but when I go to the sixth gear it moves just fine. I am worried because I dont want to destroy the engine or overwork it. Thank you